Add some simple HTMLViewer apptests.

BUILD.gn

Index: BUILD.gn
diff --git a/BUILD.gn b/BUILD.gn
index a8000b63e729c0b1fcf0d226801c64f016395344..6ef0fed59b65ad6b68d84a13d4779bb29a1766c7 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -562,6 +562,9 @@ group("gn_mojo_targets") {
       "//media/mojo/interfaces:interfaces_python",
       "//media/mojo/services:cdm_service",
       "//media/mojo:tests",
+      "//mojo/services/html_viewer:tests",
+      "//mojo/services/html_viewer:apptests",
+      "//mojo/services/network:apptests",
       "//net/interfaces:interfaces_dart",
       "//net/interfaces:interfaces_python",
       "//third_party/mojo/src/mojo/edk/js/test:js_integration_tests",
@@ -575,13 +578,6 @@ group("gn_mojo_targets") {
       "//third_party/mojo_services/src/window_manager/public/interfaces:interfaces_dart",
       "//third_party/mojo_services/src/window_manager/public/interfaces:interfaces_python",
     ]
-
-    if (!is_debug) {
-      deps += [
-        "//mojo/services/html_viewer:tests",
-        "//mojo/services/network:apptests",
-      ]
-    }
   }
 }